High-entropy engineering unlocks high-voltage redox chemistry in NASICON-type Na3.25V1.44Fe0.25Mn0.25Mg0.02Nb0.02Zr0.02(PO4)3 cathodes for advanced sodium-ion batteries

High-voltage vanadium-based NASICON cathodes for sodium-ion batteries (SIBs) are fundamentally constrained by limited electronic conductivity, insufficient capacity arising from incomplete redox utilization, and structural instability during cycling. Herein, we propose a synergistic engineering strategy integrated with conductive carbon coating to address these challenges. A multi-component NASICON cathode, Na 3.25 V 1.44 Fe 0.25 Mn 0.25 Mg 0.02 Nb 0.02 Zr 0.02 (PO 4 ) 3 (HE-NVP), is rationally designed, in which Fe 3+ and Mn 2+ substitution activates the reversible high-voltage V 4+ /V 5+ redox couple, while Mg 2+ , Nb 5+ , and Zr 4+ server as structural stabilizers to reinforce lattice integrity. The resulting configurational entropy and multi-element simultaneously regulate electronic structure, accelerate Na + diffusion kinetics, and suppress structural degradation. Benefiting from these cooperative effects, HE-NVP delivers a high reversible specific capacity of 120.9 mAh g −1 at 1C with an average voltage of 3.43 V. Remarkably, it maintains 82.4 mAh g −1 after 1100 cycles at 20C, demonstrating excellent rate capability and long-term durability. In-situ X-ray diffraction reveals that Na + storage proceeds via a highly reversible hybrid mechanism involving both solid-solution and two-phase reactions, underscoring the structural resilience of the entropy-stabilized framework. This study elucidates the mechanistic role of high-entropy design in unlocking high-voltage redox activity while mitigating phase instability, offering a viable materials engineering paradigm for advanced NASICON-type sodium-ion battery cathodes.